Wire-mesh Reactor Research Articles

Devolatilization behaviour of Kolubara and Kostolac lignite (Serbia) during the combustion process: A case study

In this study the devolatization behaviour of lignite samples, of various grain sizes, on a wire mesh reactor is evaluated. Lignite samples were rapidly heated at four different temperatures (300, 500, 700 and 900 °C). The feed lignite reveals a high content of huminite, a low inertinite and liptinite contents in the Kostolac samples and a slightly higher liptinite content in the Kolubara samples. The char obtained at 300 °C and 500 °C shows slight petrographic and chemical changes. The major changes in chemical and petrographic compositions were observed in char heated at higher temperatures (700 °C and 900 °C). FTIR spectral data for both Kolubara and Kostolac lignite samples reveal a decrease in aliphatic- and oxygen­containing structures with increase in temperatures from 300 to 700 °C. The lack of aliphatic and oxygen-containing structures, the breakdown of clay minerals and negligible amount of water are detected in samples devolatilized at 900 °C where aromatic structures dominate.Huminite reflectance of initial samples confirms the low rank (lignite) of all the samples. Char of all grain sizes obtained at 300 °C and 500 °C showed very small changes in the maceral composition and reflectance value and still corresponded to lignite rank. A significant change in maceral composition and increase reflectance is observed in char obtained at 700 °C and 900 °C of all grain sizes.

Biochar gasification: Insights from pyrolysis atmospheres and gasification heating rates

Gasification is a promising technology for the synthesis of syngas and hydrogen, with char reactivity being a pivotal factor in the design of industrial gasifiers. Despite extensive studies on the gasification characteristics of biochar, the influence of the pyrolysis atmospheres on the evolution of biochar pore structure and its reactivity in gasification remains poorly understood. This study aims to bridge this gap by comprehensively investigating the effects of char preparation atmospheres (i.e., CO2, H2O, and N2) on ensuring gasification reactivities at varied heating rates. Biochars were synthesized in a horizontal tube furnace at 700 °C with a low heating rate (10 °C min−1) under three different atmospheres: N2, CO2, and H2O. Subsequent gasification reactivities were investigated using i) a thermogravimetric analyzer (TGA) at a low heating rate (10 °C min−1) and ii) a wire mesh reactor (WMR) at a high heating rate (1000 °C s−1), both under CO2 atmosphere at 950 °C. The results showed that the presence of an active atmosphere (CO2 and H2O) during pyrolysis significantly impacts the biochar’s aromaticity, crystalline structure, and surface morphology. The functional group concentration and surface area trends indicated that CO2 and H2O atmospheres during pyrolysis enhance biochar reactivity compared to the N2 atmosphere, with the highest reactivity observed for biochars produced under H2O. Furthermore, biochar gasification reactivity was markedly higher using the WMR compared to TGA, underscoring the pronounced effects of heating rate on gasification behavior. The high heating rate in WMR preserved the biochar’s porous and amorphous structure, whereas the TGA gasification encountered diffusional limitations and thermal annealing effects. These insights underscore the need to consider pyrolysis atmosphere and heating rate in gasification studies, offering a more comprehensive understanding of biochar’s behavior under practical gasification conditions.

Sodium salt surface interactions affect single particle combustion behavior of biomass, coal, and their chars

Sodium salt additions provide an effective route for tuning the combustion behavior of solid fuels. The salt-fuel surface interactions play a key role in combustion, as demonstrated by low heating rate experiments. High heating rate single particle studies have not investigated the effect of surface interactions and microstructural changes for sodium salt-treated fuels. In this work, the effect of three different sodium salt treatments were investigated on the single particle combustion characteristics of two distinct solid fuels and their corresponding chars. This approach probed the influence of microstructural changes and the formation of oxidation-resistive functional groups during high heating rate combustion. The separate characterization of biomass, coal, and their respective chars aimed at identifying the effect of sodium during different stages of combustion. The investigation encompassed Tunçbilek lignite (TL), olive residue (OR), and their fast pyrolysis chars (TLc and ORc) obtained from a wire mesh reactor at 600 °C. Both pristine and char particles were treated with Na2CO3, NaOH, and NaAlO2 to investigate the catalytic/inhibiting effects at different stages of combustion, namely, ignition, volatile combustion, and char combustion. All samples were burned as single particles at a high heating rate, WMR (1600 °C s−1). Treated OR samples provided earlier ignition reaching ∼ 0.4 s for OR-OH and shorter char combustion times around ∼ 2.8 s mg−1 for OR-CO3. On the contrary, treated TL samples depicted slightly higher ignition delay (3.0 s for TL-OH) and prolonged char combustion (11.2 s mg−1 for TL-OH) compared to TL (2.3 s, 8.2 s mg−1). Treated TLc samples also exhibited higher ignition delay due to the hygroscopic behavior of the sodium salts, which is more pronounced in TLc-OH (5.5 s). All treated chars exhibited shorter char combustion times except TLc-OH. Overall, sodium salt additions improved characteristic combustion times of biomass and chars while inhibiting those of lignites. The inhibitive effect of sodium salts on treated OR and ORc samples was more pronounced for TGA experiments due to the alkali interaction with the lignocellulosic component and a prolonged heating-up period. The findings demonstrate the importance of high heating rate characterization to accurately understand the sodium salt additions on combustion performance.

Synergistic effects and its influencing factors during co-processing of coal and biomass in a wire-mesh reactor

The study investigated the synergistic effects of co-gasification between coal and biomass at various blending ratios, temperatures, and contact conditions using a wire-mesh reactor. This reactor ensured high heating rate and relatively separated particles at all times. The influence of biomass volatiles on the co-conversion process was isolated and analyzed to evaluate their contribution to the overall synergistic effects. Results showed that the addition of biomass volatiles significantly promoted the reaction performance of the blends, leading to more efficient synergy between the two types of particles. A new indicator, ηvol, was proposed to quantify the contribution of biomass volatiles, which revealed that, at a blending ratio of approximately 10 wt%, the promotion of volatiles from biomass became more significant than catalytic effects of AAEMs as temperature increased from 700 to 1000 °C. The contact conditions between the two types of particles also influenced the synergy of the blends, with greater synergy observed when contact conditions were improved. Furthermore, the study showed that synergy was more sensitive to the distance between the particles at higher temperature. The findings suggest that enhancing the synergistic effects through improved contact conditions in co-gasification of coal and biomass could significantly improve the gasification kinetics of higher rank coals.

High pressure CO2 gasification of Morupule coal: Kinetics and morphological development of chars

A direct gasification approach, coupling pyrolysis and gasification, was employed to study the kinetics of Morupule coal gasification in CO2 using a wire-mesh reactor (WMR) at elevated pressures (up to 20 bara) and temperatures of 900 °C and 1000 °C. A novel non-destructive analytical technique based on X-Ray computed tomography (CT) was used, for the first time, in conjunction with scanning electron microscopy (SEM) to unravel the morphological evolution of pyrolysis and gasification chars produced from the WMR. Lower total volatile yields were obtained at high pressures compared to atmospheric pressure for 0 s (quenching the reaction upon reaching temperature) holding time experiments. A temperature dependence of the gasification reaction rate at elevated pressures was observed. At 900 °C, increasing the pressure beyond 10 bara did not yield a commensurate increase in the reaction rate. Further increases in pressure to 20 bara at 1000 °C led to a pronounced increase in the reaction rate. The applicability of the Langmuir – Hinshelwood (L – H) rate model was investigated and showed a suitable characterisation of the gasification kinetics driven by a CO2 chemisorption-limited reaction mechanism. X-Ray CT imagery reveal the development of an internal macroporosity produced by the explosive release of volatiles during pyrolysis. In contrast, SEM images indicate that high pressure coal gasification is characterised by the development of micropores, with a rapid consumption of the outer char surface.

Fast pyrolysis of pulverized coal at high temperatures and fuel nitrogen migration characteristics in a wire mesh reactor

ABSTRACT Pulverized coal (PC) pyrolysis is an indispensable process for coal thermal conversion and utilization. The transformation of fuel-N into fast pyrolysis is a basis for the investigation of nitrogen migration in coal combustion. In this paper, a wire mesh reactor was used to study the initial decomposition processes and to reveal the final pyrolysis yield and composition distribution during the fast pyrolysis process. Furthermore, the initial pyrolysis characteristics of PC with different ash contents were presented and compared. The results showed that both Huangling coal (with higher volatile) and Wuhai coal (with higher ash content) showed a similar trend, and the pyrolysis ratio increased with the increased pyrolysis final temperature. The pyrolysis ratio at the high heating rate was estimated to exceed that at the low heating rate by 2%–10%. With the temperature increased, the char-N yield decreased first and then tended to be stable, and most of nitrogen remained in the char (more than 55%). An increase in heating rate made the pyrolysis zone to shift toward higher temperature, and it enhanced the yields of volatile and tar as well as the proportion of tar in volatile. Besides, the heating rate increased from 10°C·s−1 to 1500°C·s−1, the yield of tar-N increased from 4% to 14% and gas-N decreased from 28% to 19%. Overall, NH3 yielded was higher than HCN, which became more apparent at high heating rates. The content of the N-6 was positively related to the coal pyrolysis ratio.

Primary release and transformation of inorganic and organic sodium during fast pyrolysis of sodium-loaded lignin

This study employs a wire-mesh reactor (WMR) to understand the primary release and transformation of inorganic and organic sodium during fast pyrolysis of various sodium-loaded lignin samples at 300–800 °C. Due to the minimization of volatile-char interactions in WMR, the overall sodium release during lignin pyrolysis is relatively low, i.e., ∼9–11% and ∼7–14% for the inorganic and inorganic sodium loaded lignin, respectively. The presence of the inorganic sodium in the condensed volatiles (so-called oil) clearly indicates the important role of thermal ejection in the release of the inorganic sodium, since sodium salts are unlikely to evaporate under current conditions. While the release of the organic sodium into oil can be due to both thermal ejection of aerosols and evaporation of low carboxylates. Despite the low sodium release, significant transformation of the inorganic and organic sodium can take place during lignin pyrolysis. For the inorganic sodium loaded lignin, the inorganic sodium decreases continuously from ∼67% at 300 °C to ∼42% at 800 °C, accompanied by a steady increase in the organic sodium (i.e., the ion-exchangeable sodium) from ∼17% at 300 °C to ∼37% at 800 °C. While for the organic sodium loaded lignin, its transformation into the inorganic sodium is faster at higher temperatures, leading to a large increase in the inorganic sodium (i.e., carbonates) from ∼9% at 300 °C to ∼48% at 800 °C, as well as a reduction in the organic sodium from ∼79% at 300 °C to ∼28% at 800 °C. The data generated in this study will be important to understand the catalytic mechanism of sodium during thermochemical processing of alkali lignin for the production of bioenergy and biofuels.

Characterization of tars from recycling of PHA bioplastic and synthetic plastics using fast pyrolysis

The aim of this study was to investigate the pyrolysis products of polyhydroxyalkanoates (PHAs), polyethylene terephthalate (PET), carbon fiber reinforced composite (CFRC), and block co-polymers (PS-b-P2VP and PS-b-P4VP). The studied PHA samples were produced at temperatures of 15 and 50 oC (PHA15 and PHA50), and commercially obtained from GlasPort Bio (PHAc). Initially, PHA samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC) to determine the molecular weight, and structure of the polymers. Thermal techniques such as thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses were performed for PHA, CFRC, and block co-polymers to investigate the degradation temperature range and thermal stability of samples. Fast pyrolysis (500 oC, ∼102 °C s−1) experiments were conducted for all samples in a wire mesh reactor to investigate tar products and char yields. The tar compositions were investigated by gas chromatography–mass spectrometry (GC–MS), and statistical modeling was performed. The char yields of block co-polymers and PHA samples (<2 wt. %) were unequivocally less than that of the PET sample (~10.7 wt. %). All PHA compounds contained a large fraction of ethyl cyclopropane carboxylate (~ 38–58 %), whereas PAH15 and PHA50 additionally showed a large quantity of 2-butenoic acid (~8–12 %). The PHAc sample indicated the presence of considerably high amount of methyl ester (~15 %), butyl citrate (~12.9 %), and tributyl ester (~17 %). The compositional analyses of the liquid fraction of the PET and block co-polymers have shown carcinogenic and toxic properties. Pyrolysis removed matrices in the CRFC composites which is an indication of potential recovery of the original fibers.

On the primary pyrolysis products of torrefied oak at extremely high heating rates in a wire mesh reactor

Torrefaction is a key process for biomass energy densification ahead of its utilisation in pyrolysis, gasification or combustion, and therefore the changes it originates have been the subject of multiple studies. Most of them employ low heating rates, in the range of thermogravimetric analysers (TGA), typically below 1 °C s−1 or high rates (100–1000 °C s−1) in reactors where tars undergo considerable secondary reactions following release from a particle and the temperature history of the sample is not well defined, such as entrained flow or fluidised beds. This study aims to analyse the behaviour of torrefied lignocellulosic biomass (oak) under fast pyrolysis in with very controlled temperature history and absence of secondary reactions between evolving volatiles and chars in a wire mesh reactor (WMR), which allows determination of primary products. To this end, oak was firstly torrefied in a grey-King reactor to provide samples from mild to severe torrefaction (210–300 °C). The raw and torrefied oaks were pyrolyzed/gasified, at 1000 °C s−1 and 850 °C in the WMR using He and CO2 atmospheres. All samples showed high volatile production, in excess of 80 wt.%, but with a clear drop with increasing torrefaction temperature. The char yields from the WMR in CO2 were lower than in He, reflecting a degree of char gasification. However, char deactivation at the higher torrefaction temperatures caused a sharp decrease in the extent of gasification from 32 wt.% for Raw Oak to 6 wt.% for oak torrefied at 300 °C (Oak-300). This is a consequence of the predominance of chemical effects such as enrichment of carbon, which increased from 46.5 wt.% for Raw Oak to 54.3 wt.% in Oak-300 and depletion of oxygen, which led to greater aromaticity and structural order in the char with torrefaction temperature, over physical changes observed by scanning electron microscopy (SEM) revealing increasing porosity.

The effect of torrefaction, slow, and fast pyrolysis on the single particle combustion of agricultural biomass and lignite coal at high heating rates

The present paper studies single particle combustion of olive residue (OR), almond shell (AS), and Tunçbilek lignite (TL) and their thermal pre-treated particles in a vertical wire mesh reactor (WMR) setup. Pre-treatment of the fuels was done via torrefaction, slow, and fast pyrolysis. The particles with different masses were heated to 1000 °C by radiation with a heating rate of 900 °C/s. The combustion process was recorded with a high-speed camera. The time analysis demonstrated that the particle mass and size did not affect ignition delay time; however, slow pyrolysis had a significant effect on the ignition delay time. The ignition delay time was significantly increased for the chars produced from slow pyrolysis compared to raw and other heat-treated particles for all fuels. Burnout times of all fuels increased proportionally with particle mass. Fast and slow pyrolysis generally increased the char combustion and burnout times. The average burnout times for fast and slow pyrolyzed biochars were ∼20 s and ∼29 s, respectively, while those of raw biomass were ∼9 s. The average burnout times for fast and slow pyrolyzed lignite particles was ∼20 s and ∼53 s, respectively, while those of raw lignite was ∼19 s, when 2 mg particles were compared. Fast pyrolyzed biomass particles had similar burnout times compared to those of raw TL particles. This depicts the potential of co-firing TL with biomass chars produced from fast pyrolysis.

Solar-TiO2 immobilized photocatalytic reactors performance assessment in the degradation of methyl orange dye in aqueous solution

Heterogeneous photocatalysis with titanium dioxide (TiO2) nanoparticles (NPs) has been demonstrated an emerging semiconductor material and widely been used in the treatment of wastewater due to is its high photocatalytic activity. In this study, TiO2 NPs with and without hydrolysis were synthesized by sol–gel and heat treatment methods. About 67 times higher surface area was obtained for TiO2 NPs synthesized with hydrolysis as compared to without hydrolysis. The X-ray diffraction showed an increased amount of anatase phase of TiO2 NPs with hydrolysis whereas the rutile phase of TiO2 NPs was obtained without hydrolysis. Immobilized-TiO2 NPs borosilicate glass (BG), cement coated borosilicate glass (CCBG), and steel wire mesh (SWM) reactors were constructed and the photocatalytic performance of TiO2 NPs was investigated to the degradation of methyl orange (MO) dye under solar irradiation. The photocatalytic removal of 10 mg/L MO dye was 97.8%, 88.6%, and 21.5%, respectively, at the same dose of immobilized-TiO2 on BG, CCBG, and SWM surfaces at pH 6.2 with 5 h of contact time. The kinetic study showed a pseudo-first-order reaction model fitted the best for MO dye removal. The increase of dye concentration decreases the performance of BG reactor, whereas, the addition of oxidant H2O2 increases the performance of BG reactor. The lowest TiO2 NPs loss from the study was observed for BG reactor (10.78%). This study indicates that the solar-TiO2 immobilized borosilicate glass reactor has high potential in the treatment of toxic compounds in textile wastewater.

A collection of model parameters describing the gasification behavior of different fuels under entrained flow conditions

Entrained flow gasifiers can be fed with a variety of fuels. However, each fuel has its own gasification behavior resulting in different operating conditions and ideal design configurations. The optimum can be determined by e.g. modelling and simulating their gasification behaviors. Therefore, models and their parameters are necessary, which consider the processes involved. A collection of model parameters describing results of experimental investigations under entrained flow gasification is included in the presented “Solid Fuel Entrained Flow Gasification Database”. The database contains information about devolatilization, surface area development, thermal deactivation and the reaction kinetics including product gas inhibition of five lignites, five bituminous coals, one anthracite, two pretreated biomasses and one blend. Their determination in a wire mesh reactor, a pressurized high temperature entrained flow reactor, a structural analyzer and thermogravimetric balances is exemplary presented by four investigated fuels. Further the content of the database is explained and visualized by comparing the results with ten other fuels. Overall, the presented database is unique in its kind as it summarizes these insights and supplements it with further information. There is no other fuel database available, which covers model parameters and refers to validation data of such a broad range of fuels considering entrained flow gasification.

Bifurcation analysis of oxidative coupling of methane in monolith, gauze or wire-mesh reactors

We use a multi-scale multi-mode reduced order model for coupled homogeneous-catalytic reaction systems to present a comprehensive bifurcation (ignition-extinction) analysis of the oxidative coupling of methane (OCM) in monolith, gauze or wire-mesh type reactors. We determine the impact of methane to oxygen ratio in the feed, space time, channel hydraulic radius (or gas phase to catalyst volume ratio), washcoat diffusional limitations, operating pressure and substrate thermal conductivity on the ignition and extinction behavior of the system as a function of the feed temperature. The computations show that for typical operating conditions, the methane conversion and C2 product selectivity are non-monotonic on the ignited branch and there exists an optimum point of operation away from the extinction point. The predicted methane, oxygen conversions and C2 selectivity are compared to reported experimental results in the literature. We also present the various species and temperature profiles along the length of the reactor and examine how these profiles are impacted by the substrate conductivity, space time and heat loss. The results obtained for monolith, gauze or wire-mesh reactors are compared to those in packed-bed reactors and suggestions are provided for scale-up and optimization of these reactors for carrying out OCM as well as other catalytic partial oxidations.

The pyrolysis of lignin: Pathway and interaction studies

Three different lignin samples (alkali lignin, THF separated lignin) and hemicellulose removed biomass samples were pyrolyzed at various temperatures and heating rate in a wire mesh reactor (WMR). The product distribution and characterisation of liquid product were analyzed and compared to obtain the pyrolysis behavior of lignin and the possible interaction. Different reactivities were observed for the studied components. The pathway of lignin pyrolysis was proposed. Heating rate and temperature played a significant role on the lignin and biomass pyrolysis. At intermediate temperatures of 450–525 °C, the phenols in liquid products were at maximum, while lower and higher temperatures promoted to the formation of dimer compounds in liquid product·THF soluble lignin favored the production of liquid, while THF insoluble lignin mainly formed solid residues. The interaction between THF separated lignin can promote the formation of phenols through the cracking of carboxylic acid, ketone and aldehyde and inhibit the coupling reaction of free radicals into dimer compounds. An interaction between lignin and cellulose was also observed leading to a lower solid residue but a higher yield of liquid. The interaction between lignin and cellulose also promoted the secondary decomposition of guaiacol derivates forming new compounds such as benzene, phenol and p-xylene and inhibited the condensation reaction of lignin.

Fast Pyrolysis of Pulverized Coal at High Temperatures and Fuel Nitrogen Migration Characteristics in a Wire Mesh Reactor

Fast Pyrolysis of Pulverized Coal at High Temperatures and Fuel Nitrogen Migration Characteristics in a Wire Mesh Reactor

Prediction of yields and composition of char from fast pyrolysis of commercial lignocellulosic materials, organosolv fractionated and torrefied olive stones

This study investigated the fast pyrolysis behaviour of torrefied olive stones, fractionated olive stones and lignocellulosic commercial compounds. Olive stones were reacted in a continuous industrial torrefaction unit. The olive stones were also fractionated into their main components in an organosolv reactor at temperatures from 170 to 190 °C in both the presence and absence of an acidic catalyst. All samples were reacted in a wire mesh reactor at different temperatures (800–1150 °C) and heating rates (400–1150 °C/s), and the solid product was characterised for its yield, morphology, and elemental composition. The char yields from fast pyrolysis of commercially available cellulose, hemicelluloses, and lignin were compared with yields of fractionated olive stones. A model was developed to compare the measured yields of olive stones with the predicted yields using fractionated or commercial components. The presence of acid during fractionation had a stronger effect than the temperature, particularly on the lignin fraction. The fractionated lignocellulosic compounds provided more accurate predictions of the char yields of olive stones, as compared to the commercial lignocellulosic compounds. The fractionation at 180 °C without acid catalyst gave the cellulose, hemicellulose, and lignin with highest degree of purity and resulted in the most accurate predictions of the experimental yields of olive stones. The results showed that interactions between the lignocellulosic components were not significant. The char yield of each fractioned compound and non-treated olive stones could be accurately predicted from the lignocellulosic content which has importance for biorefinery applications in which each fraction is used as a value-added product.

Early-stage kinetics and char structural evolution during CO2 gasification of Morupule coal in a wire-mesh reactor

Understanding the intrinsic gasification kinetics and structural evolution of char is crucial in the effective design of industrial gasifiers. This work studies the kinetics of Morupule coal gasification in atmospheric pressure CO2 at isothermal temperatures of 900–1050 °C using a rapid heating wire-mesh reactor (WMR). The gasification reaction order was determined by varying the concentration of CO2 in the reactor atmosphere. The bulk chemical structure and surface chemistry of the early-stage residual chars were characterised using Raman and X-Ray photoelectron spectroscopy, respectively. Gasification reaction rates were significantly higher than those presented in published literature with an activation energy of 320 kJ mol−1 and a pre-exponential factor in the order of 1010 s−1. In a chemical reaction controlled kinetic regime, the reaction order was found to be zero and increased to 0.6 in a mixed chemical reaction plus pore diffusion controlled kinetic regime. The bulk chemistry of the chars was largely unaffected by CO2 in the conversion range studied. However, surface chemistry analyses revealed a decrease in the carbon content, through the depletion of CC/CC bonds, resulting in the development of char surface porosity. Residual chars from gasification experiments showed a lower combustion reactivity to those produced under inert pyrolysis conditions. This study provides insights on direct gasification (i.e. no char preparation in a separate pyrolysis stage) for kinetic determinations and a concomitant extensive characterisation of char structural properties.

Formation of reaction intermediates and primary volatiles during acid-catalysed fast pyrolysis of cellulose in a wire-mesh reactor

This study aims to understand the fundamental reaction mechanisms during fast pyrolysis of the acid-impregnated cellulose in a wire-mesh reactor at 40–450 °C and 20 °C/s, via quantifying key compounds in the reaction intermediates and primary volatiles. Acid impregnation reduces the onset reaction temperature of cellulose pyrolysis. During acid-catalysed cellulose pyrolysis, 1,6-anhydro-β-d-glucofuranose (AGF), levoglucosenone (LGO) and 5-hydroxymethylfurfural (5-HMF) are identified as major products in the primary volatiles, and the formation of levoglucosan is greatly suppressed. At temperatures < 100 °C, acid catalyses hydrolysis reactions to produce glucose, which is further dehydrated to AGF at 120 °C. At temperatures > 160 °C, acid enhances the dehydration of glucose, levoglucosan and AGF to produce 5-HMF and LGO as major primary products. Once produced, those products can be easily released into the vapour phase, as either aerosols via thermal ejection or vapours via evaporation. As the pyrolysis temperature increases to 240 °C, aromatic compounds can be identified in the primary volatiles, indicating condensation reactions also play important roles during acid-catalysed cellulose pyrolysis under the conditions. As a result, char formation becomes the favoured pathway during acid-catalysed cellulose pyrolysis at temperatures > 300 °C.

Linking char reactivity to structural and morphological evolution during high pressure pyrolysis of Morupule coal

Understanding the influence of pressure on char physicochemical properties and reactivity during pyrolysis is principal for the design and optimisation of coal gasification technologies. This work investigated the pyrolysis behaviour of Morupule coal at various pressures and temperatures in a high-pressure wire-mesh reactor (HPWMR). The effect of pressure was pronounced at 600 and 800 °C, resulting in lower total volatile yields at higher pressures due to the repolymerisation of volatiles. Although graphitisation was limited during the heating period, an increase in the concentration of ordered structures was observed during holding at 1000 °C. Marked blowholes on the char surface suggested an explosive bubble transport phenomenon during pyrolysis. Chars produced during the ramping period under high pressure showed higher combustion reactivities than their low-pressure counterparts. However, prolonged holding at peak temperature produced chars of similar reactivity, with their CO2 gasification reactivity found to be independent of pyrolysis pressure.

Experimental and kinetic modelling investigation on the effects of crystallinity on cellulose pyrolysis

The present work studies the effects of the crystallinity level of cellulose on the primary reactions during the slow and fast pyrolysis conducted in a wire-mesh reactor at 40 °C/min and 6000 °C/min, respectively. The sugars present in the water-soluble intermediates were analysed in a chromatogram equipped with a Q-exactive high-resolution mass spectrometer. The products in the washed primary tars were quantified through GC/MS. Slow pyrolysis experiments were also performed in a thermogravimetric analyser at four different heating rates (5, 10, 20 and 40 °C/min). All experimental data was used to develop a modified kinetic model that considers the effects of crystallinity on cellulose pyrolysis, which is based on the cellulose sub-mechanism of the Bio-PoliMi kinetic model. The kinetic parameters of each reaction in the modified model were calibrated using a two-step fitting procedure. The experimental results show that low crystallinity promotes the dehydration reactions in the cellulose solid base and the formation of oligosaccharides in the water-soluble reaction intermediates, increasing the formation of furans and decreasing that of levoglucosan in the final primary tar. The effect of crystallinity on the pyrolysis characteristics of cellulose is weaker during fast pyrolysis than during slow pyrolysis. The isoconversional kinetic approach of cellulose pyrolysis presents a low initial activation energy of the pyrolysis of amorphous cellulose, which is close to the activation energy of cellulose hydrolysis. Assuming that the amorphous region of cellulose decomposition path prefers depolymerization through hydrolysis accompanied by the dehydration of nearby hydroxyl group, the modified kinetic model succeeds to predict the effect of crystallinity on the thermal stability and the yields of char, levoglucosan and furans during cellulose pyrolysis.